This invention relates to a fluid actuated traction motor, and is more particularly concerned with a device which contracts axially when a fluid pressure is applied to it so as to apply a tensive force, over a cable or similar tendon, to an object to be pulled.
The invention is also directed to a pneumatic or hydraulic muscle which can be incorporated within an elongated insertion tube of a borescope or like device for articulating its articulation or steering section, so that the use of extremely long steering cables can be avoided.
A borescope is generally characterized as an elongated flexible insertion tube with a viewing head at its distal or forward end, and a control housing at its proximal end for controlling or steering the forward end. Such a borescope has a bendable-tube steering section or articulation section at the distal end adjacent the viewing head. One or two pairs of control cables extend through the articulation section, and then through the remainder of the flexible insertion tube. These cables connect with a steering control in the control section. One or both pairs of these cables are differentially displaced to bend the articulation section. The viewing head can thus be remotely oriented to facilitate the inspection of an object. Borescopes are intended for visual inspection of mechanical devices such as jet engines or turbines, where it would be difficult or impossible to examine the device's internal elements directly. The borescope needs to go into narrow tortuous passageways, and must observe similar bending and steering considerations. In addition the pathway to the object can be quite long, and so it is often necessary that the borescope insertion tube be fifteen meters or more in length.
Endoscopes are similar devices, but are intended to be inserted into a body cavity, such as the colon or esophagus, for visual investigation of tissues within the cavity.
A number of types of cable actuated articulation or steering mechanisms are known, and typical ones are discussed in U.S. Pats. Nos. 3,610,231; 3,739,770; 3,583,393; 3,669,098; 3,799,151; and 4,347,837. Another steering mechanism is described in U.S. Pat. No. 4,700,693, filed Dec. 9, 1985, and having a common assignee herewith.
The articulation mechanisms for those previously-proposed endoscopes and borescopes require that the cables have a significant amount of slack or play because the articulation sections bend at discrete points rather than follow a smooth curve. However, in both the borescope and endoscope, the articulation section must be bent rather precisely in order to obtain the desired penetration without damaging delicate engine parts or injuring the patient's tissues. For these reasons cable tension must be limited and cable slack must be minimized. Where the insertion tube is long, cable slack is also included to accommodate cable tightening due to coiling and bending of the insertion tube through which the steering cables pass.
Also, when the cables are differentially displaced to effect articulation, the cable displacement is not precisely reciprocal. That is, the motion of one cable is not the exact opposite of the other. This fact results in undesirable tensioning at some times and at other times produces unwanted cable slack, which can lead to imprecise steering. Coiling of the insertion tube can produce high tension in both cables of a cable pair, which can lead to increased friction and damaging high forces on the cables and on the articulation section. If no measures are taken to compensate for this, early failure can follow.
Ideally, the steering cables should be kept short to avoid the above problems. To do this, the cables would have to terminate within the insertion tube near the articulation section, and some mechanism to draw the cables would be incorporated within the sheath of the insertion tube. Unfortunately, no known existing mechanism has been proposed for this task.
In the field of pneumatic or hydraulic devices, a fluid traction cylinder has been proposed in U.S. Pat. No. 3,570,814, for the purpose of producing a contraction or shrinking of various enclosures. There a cylinder with axial folds is wound with straps. The diameter of the cylinder increases as air pressure is applied, which tensions the straps. The device cannot be made to contract axially.